1. Field of the Invention
This invention relates generally to communication systems and more particularly, but not by way of limitation, to communication systems having an intercommunication (intercom) network and a telephone exchange network whereby two-way communication can be maintained between the calling station and the called station or stations via the telephone exchange network, such as a private automatic branch exchange.
2. Description of the Prior Art (Prior Art Statement)
The following statement is intended to be a prior art statement in compliance with the guidance and requirements of 37 C.F.R. .sctn..sctn.1.56, 1.97 and 1.98.
Several intercom networks are known to be, or to have been, used. These networks are believed to be classifiable in one of two categories. The first category includes those systems having customized telephones which include special built-in electronic circuitry. The second category includes those types of systems which have large boxes or housings used in addition to the telephones with which such systems are used.
Regardless of the classification, however, these presently known types generally use unbalanced lines to interconnect the individual local stations with a central control unit. Also, each of these types uses various types of electronic switching circuits to perform the necessary functions of interconnecting the calling and called stations.
These systems generally indicate the need for some type of intercommunication network. More particularly, our present manner of living creates the need for intercommunication networks in such places as the home, business and hospital so that rapid communication may be spread to diverse and distant locations.
To satisfy such needs in an economically feasible manner, there is the further need to utilize ordinary telephones which are normally present in such places as the home, business and hospital. Furthermore, it is important that the intercom network be simple to install so that installation and service costs may be kept to a minimum. It is also important that the intercom network be compatible with private automatic branch exchanges (PABX) or similar telephone systems so that the intercommunication network may be integrated with the PABX or other type of telephone exchange network.
Although these needs are important, it is also important to provide an intercom network which provides relatively high quality audio so that the communications can be understood. Furthermore, there is the need that the network be versatile so that either individual or multiple stations may be addressed and also so that the communication can be broadcast in either a conversational level or a power amplification level. In such a versatile network wherein either an individual station or a plurality of stations may be called, it is important to provide the conversational level with separate output level controls so that one level can be used when the communication is between only the calling and a single called station, for example, and a separate level can be used when all of the stations are being addressed.
Still another need is to provide an intercommunication network which permits two-way conversation. To provide such a two-way network creates the further need for the system to have a talk channel and a listen channel which are interconnected to prevent lock up in either the listen or the talk modes. Furthermore, such interconnected channels raise the need for a built-in balance detector to test and set the balance for the least power feedback between the talk and listen channels. Another need in such a two-way network is the provision of apparatus for generating warning, or notification, signals to advise local stations that have been called that they are actively connected to a calling station.
In addition to these many needs, there is the need for apparatus within the intercommunication network whereby a central operator may directly select and communicate with any one or more of the various local stations.
Additionally, it is known that telephone exchange networks, such as private automatic branch exchanges, have been proposed or developed. Such proposals or developments indicate the need for private telephone exchanges. There is the further need of combining such telephone exchange networks with intercom networks to provide an overall communication system.
Although as previously stated, there have been various types of intercommunication networks and telephone exchange networks proposed, it is believed that each of such systems has the shortcoming of failing to meet, either individually or in combination, each and every one of the above-stated needs.